Polycarbonates are well known as a tough, clear, highly impact resistant thermoplastic resin. However the polycarbonates are also possessed of a relatively high melt viscosity. Therefore in order to prepare a molded article from polycarbonate, relatively high extrusion and molding temperatures are required. Various efforts throughout the years to reduce the melt viscosity while also maintaining the desired physical properties of the polycarbonates have been attempted. These methods include the use of plasticizers, the use of aliphatic chain stoppers, reduction of molecular weight, the preparation of bisphenols having long chain aliphatic substituents and various polycarbonate copolymers as well as blends of polycarbonate with other polymers.
With respect to plasticizers, these are generally used with thermoplastics to achieve higher melt flow. However usually accompanying the plasticizer incorporation into polycarbonate compositions are undesirable features such as embrittlement and fugitive characteristics of the plasticizer.
Increased flow can be fairly readily obtained with the use of aliphatic chain stoppers, however impact resistance as measured by notched izod drops significantly. Embrittlement may also be a problem.
When utilizing a bisphenol having a lengthy aliphatic chain thereon, increases in flow can be observed. However these are usually accompanied by substantial decreases in the desirable property of impact strength. utilizing a copolyestercarbonate with an aliphatic segment, processes such as the pyridine solvent process of U.S. Pat. No. 3,169,121, have been utilized as well as processes utilizing diacid halides in an interfacial process sequence such as disclosed in U.S. Pat. No. 4,238,596 and U.S. Pat. No., 4,238,597 Additionally, high molecular weight aliphatic segments have been introduced into the polycarbonate (by interfacial methods) utilizing dicarboxylic endcapped polyisobutylene segments, see Mark and Peters U.S. Pat. No., 4,677,183 and U.S. Pat. No. 4,628,081. Additionally a method of incorporating aliphatic dicarboxylic acids into polycarbonate is disclosed in Kochanowski, U.S. Pat. No., 4,280,683 wherein in an interfacial process the diacids are reacted together with a dihydric phenol and a carbonate precursor such as phosgene.
As disclosed in the companion case filed on the same day and designated as 8CL-6888, the incorporation of aliphatic alpha omega medium chain acids of from eight to twenty carbon atoms produced copolyester-carbonates of sharply increased processability as measured by melt flow together with a property spectrum which was at least substantially similar to the usual aromatic polycarbonate. Therefore great interest has been generated in successfully synthesizing the copolyestercarbonate with the aliphatic ester segment. Although a standard interfacial process utilizing the chloride derivative of the saturated aliphatic alpha omega diacids can be employed to prepare the copolyestercarbonate the availability of the diacid chloride starting materials is a problem. Aliphatic diacid chlorides are commercially available only in limited quantities and at a very high cost. Furthermore even high purity diacid chlorides contain color contaminants which cause the final molded parts to display an unattractively high yellowness index. Therefore attention was focused on the readily available, relatively inexpensive diacid starting materials. The previously mentioned Kochanowski patent was studied. The disclosure is directed to the usage of various aliphatic dibasic acids as disclosed at column 5, lines 13 through 22 in combination with a dihydric phenol and a carbonate precursor such as phosgene in an interfacial process. According to Kochanowski at column 6, lines 24 to 31, the reaction was carried out at a pH of between about 4.5 and 8, preferably between about 5.5 and 6.5 until the dibasic acid is consumed. The pH of the reaction is then raised to a value of between 9 and 11.5 to complete the reaction. The polyestercarbonate is isolated according to standard techniques, see column 6, lines 24 through 30 of Kochanowski Experiments which followed the Kochanowski disclosure were conducted. 50% of adipic acid present as a 10 mole % reactant was incorporated within the polycarbonate backbone therefore providing a 5 mole % copolyestercarbonate. Additionally it has been discovered that the preferred pH range disclosed in Kochanowski does not bring about complete incorporation of diacids into copolyestercarbonates in a reasonable time period. The procedure of Example 6, see column 9, lines 1 to 13 of Kochanowski, discloses the preparation of an azelate containing bisphenol-A copolyestercarbonate. The azelaic acid reactant was present at 25 mole percent of the bisphenol-A. The most incorporation of azelate observed was 18 mole % following the procedure of Example 6. It is therefore clear that in many situations, the dibasic acid cannot be consumed in a practical sense. The raising of the pH therefore should not occur according to the Kochanowski disclosure. It should also be noted that Kochanowski uses a very high excess of phosgene
A new process has been discovered which can about complete incorporation of aliphatic alpha omega diacids into aromatic polycarbonate backbones thereby producing a copolyestercarbonate having a predictable quantity of ester. A new pH stepwise range is followed to obtain copolyestercarbonate wherein there is essentially no detectable unreacted dicarboxylic acid which contaminates the waste product stream or the resultant polymer. The excess of phosgene employed in Kochanowski can be substantially reduced.